1. Field of the Invention
The present invention relates to an image sensing apparatus, image sensing apparatus control method, and imaging system.
2. Description of the Related Art
An image sensing apparatus such as a MOS sensor includes a pixel array in which a plurality of pixels are arrayed, a readout unit which reads out a signal from a selected row (readout row) in the pixel array and outputs a plurality of signals, and an output unit which outputs an image signal in accordance with a plurality of signals output from the readout unit. The output unit performs correlated double sampling (to be simply referred to as CDS hereinafter) processing.
The readout unit reads out an optical signal and noise signal at different timings from a pixel on each column on a readout row in the pixel array, and temporarily holds the two signals in a line memory. The readout unit outputs the optical signal and noise signal held in the line memory to an optical signal output line (to be referred to as an S output line hereinafter) and noise signal output line (to be referred to as an N output line hereinafter) in the output unit. The readout unit sequentially performs this operation for respective columns.
In the output unit, a difference circuit arranged on the subsequent stage of the S and N output lines calculates the difference (performs CDS processing) between an optical signal transferred to the S output line and a noise signal transferred to the N output line. The difference circuit sequentially outputs the image signals of pixels on respective columns.
Assume that an optical signal and noise signal are output from a pixel on the first column to the first S output line and first N output line, respectively, and an optical signal and noise signal are output from a pixel on the second column to the second S output line and second N output line, respectively. In this case, the first difference circuit calculates the difference (performs CDS processing) between an optical signal output to the first S output line and a noise signal output to the first N output line, outputting the image signal of the pixel on the first column. The second difference circuit calculates the difference (performs CDS processing) between an optical signal output to the second S output line and a noise signal output to the second N output line, outputting the image signal of the pixel on the second column. This arrangement can increase the operation speed of the output unit because operations for an optical signal and noise signal can be parallelly executed for the first and second columns.
In this arrangement, the first S output line and first N output line correspond to pixels on the first column, and the second S output line and second N output line correspond to pixels on the second column. Thus, the first S output line, first N output line, second S output line, and second N output line are generally arranged in the order named.
The first S output line, first N output line, second S output line, and second N output line are generally juxtaposed to each other. However, it is known that adjacent output lines are capacitively coupled and cause crosstalk and decrease the signal-to-noise ratio. In contrast, in an image sensing apparatus disclosed in Japanese Patent Laid-Open No. 2005-217366, shielding lines and shielded pins are interposed between output lines in an arrangement in which the first S output line, first N output line, second S output line, and second N output line are arranged in the order named. According to Japanese Patent Laid-Open No. 2005-217366, capacitive coupling between output lines can be suppressed.
In a technique disclosed in Japanese Patent Laid-Open No. 60-183784, lines for transferring a signal are juxtaposed, and dummy lines are arranged on the two sides of the line group. According to this technique, any line is arranged between lines or between a line and a dummy line. This arrangement can remove variations of the line distributed capacitance, and increase the readout precision of a photoelectric conversion device.
Disturbance noise sometimes influences a solid-state image sensing apparatus. For example, if disturbance noise acts on an output line, the precision of a signal output from the solid-state image sensing apparatus may degrade. However, measures against disturbance noise have been examined in neither of Japanese Patent Laid-Open No. 2005-217366 nor 60-183784 examines.